Alkaline earth yttrate luminescent materials



U.s. Cl. 252-3015 10 Claims ABSTRACT OF THE DISCLOSURE Binary barium 'yttrates and ternary barium-magnesium, barium-calcium, and barium-zinc yttrates, each activated with the rare earths dysprosium, samarium, terbium, or preferably europium form phosphors with emissions characteristic of the rare earth used, and are useful in lamps and color television.

' Cross-references to related applications This application is a continuation-in-part of copending application Ser. No. 468,810, Mary V. Hoffman, filed July 1, 1965, now abandoned.

Background. of the invention The present invention relates to luminescent materials. More particularly, it relates to alkaline earth yttrate phosphors useful in discharge lamps and cathode-ray tubes.

Improvements'and particular characteristics have long been sought in red emitting phosphors, both for use in improving the whiteness and color rendition of the light output of high pressure mercury vapor lamps and for use in cathode-ray tubes such as for color television.

Phosphors of manganese-activated magnesium fluorogermanate, of tin-activated strontium magnesium orthophosphate and of europium-activated yttrium orthovanadate have been used for adding a red component to the light output of high pressure mercury vapor lamps, thus improving the color of the light emitted and giving better color rendition.

Summary of the invention It is an object of the present invention to provide new and improved red-emitting phosphors. suitable for use in the color correctionof high pressure mercury vapor discharge lamps and for use in cathode-ray-tube applications.

Further objects and advantages of the invention will appear from the following detailed description of species thereof.

Briefly stated, according to one aspect of the present invention, I have discovered new 'and improved luminescent materials of barium yttrates, which are binary :compounds, and of barium-magnesium .yttrates,.- bariuin-calcium yttrate, and barium-zinc yttrate, which. are ternary compounds, each activated with certain rareearths and, more specifically, luminescent materials having the following molar composition:

aBaOzbAO: (c-d) Y O :dR O wherein: A is selected from the groupv consisting of Mg, Ca and Zn, R is selected from the group consisting of Eu, Dy, Sm

and Tb, i a is either between about 0.8 andv 1.2 or between about 1.6 and 2.4, when a is between about 0.8 and 1.2, b is zero,-and when a is between about 1. 6 and 2.4, b is between about 0.8

and 1.3,

' United States Patent 3,450,643 Patented June 17, 1969 i c is between about 0.8 and 1.3, and

d is between about 0.008 and 0.2.

More specific embodiments of the invention include the binary phosphor wherein b is zero and the ternary phosphors wherein a is between about L6 and 2.4 and b is between about 0.8 and 1.3. Preferred embodiments include these specific binary and ternary phosphors in which c is between about 1.00 and 1.25 and d is between about 0.008 and 0.14 with R being Eu. Further preferred embodiments provide for R being Eu, c being about 1.00, and 0. being about 0.05.

Preferred activators with the various phosphors are as follows:

when A is 'Zn, R is Eu, Dy, Sm or Tb; when A is Ca, R is Eu; and when A is Mg, R is Eu or Sm.

Dy, Sm and Tb activators give better response to cathode-ray excitation than to ultraviolet radiation excitation.

Description of the preferred embodiments Ba ZnY- O and Ba CaY O have been isolated and found to be stable under normal atmospheric conditions. In the BaO:ZnO:Y O system, another ternary compound exists, but it is not stable and therefore does not make a prac. tical phosphor.

Binary phosphors with a ratio of Y O /BaO higher than 1.0 will contain (YR) O as a second phase, which is also an efficient phosphor under 2537 A. excitation. Samples with a ratio less than 1.0 will contain BaO as a second phase. This material would not 'contributeto fluorescence and is deleterious because it is hydroscopic: If present in the phosphor, it will possibly cause problems in suspension preparation or in lamp stability. The compound BaY O is found exclusive of other phases only at a ratio of 1.0, but in order to avoid the possible presence of deleteriously hydroscopic B210, a ratio of is the preferred binary composition. Likewise for the Value of d:

ternary phosphors, slight excesses of ('YR) O are desirablefor the same reasons. This can be specified 'as a+b3 and g1.

The variation of brightness with 'Eu O content has been determined for binary BaY OgzEu and is shown in the following table for the formula I From these data, 5 mole percent Eu O is chosen as the preferred composition. 1 1 Composition variations have been tried to determine if substitutions can be made in the phosphors of the invention. It was determined that small additions (1%) of Er, Gd, Sb and Bi, are definitely harmful to the phosphor brightness. Significant amounts of impurities are likely to be harmful.

Manufacturing procedure.-The preferred starting materials for these phosphors are BaCO BaF ZnO, CaCO MgO or compounds which give these materials on firing and Y O which contains the desired amount of Eu O or Whatever rare-earth activator is used. This is obtained by dissolving Y O and the desired rare-earth activator intdilute nitric acid, coprecipitating these as the oxalate by addition of oxalic acid, and then firing to form (YR) O This can then be mixed with the other componentsby conventional means, such as ball milling, with assurance that the activator is thoroughly distributed in the composition. If the two oxides Y O and R are used separately, it is difficult to obtain uniform material.

Phosphors have been fired at temperatures between 1000 C. and 1350 C. for from 2 to 16 hours. The preferred firing schedule is 1150 C. for 2.5 hours for the binary compounds and 16 hours for the ternary compounds.

As with many phosphor reactions, the formation of BaY O is improved by the use of a fluxing agent. Fluorides and chlorides are commonly used and in this case, it was found that the use of 5 mole percent was sufficient to give good 'brightnesses in reasonable firing times. Amounts at least as high as mole percent of both fluorides and chlorides were used with no further advantage. In the ternary compounds, the fiuorides are preferably not used, but longer firing temperatures are required.

These studies have led to the following standard phosphor batch formulation in mole ratio which gives a good brightness with reasonable firing conditions such as 1150 C. for 2% hours.

0.95 BaO 0.05 BaF 1.05 o.95 o.5)2 3 For IOOO-gram batches to make BaY O :Eu this corresponds to:

370.7 gm. BaO

21.9 gm. BaF 563.0 gm. (Y) O 43.9 gm. Eu O Preferably combined by coprecipltation as (YE\1)2O3.

Other activators would be used in proportional molar quantities and in the same manner.

The following batch formulation is satisfactory for giving Ba Zn(YR) O phosphors of the invention when fired at 1060 C. for 16 hours.

gm. 4.0 gm. ZnO 19.5 gm. BaCO For each of these examples, (YR) O contains the desired activator, preferably co-precipitated as the oxalate and fired to the oxide form. Eu, Tb, Sm and Dy can be added this way.

The Ba Mg(YR) O and Ba Ca(YR) O phosphors would be made similarly from the folowing batch formulations, respectively:

11.25 gm. (YR) O 2.0 gm. MgO

19.5 gm. BaCO and 5.0 gm. CaCO 19.5 gm. BaCO Optical data.-In a high pressure mercury vapor lamp test, BaY O:0.05 -Eu O gave 53.5 lumens per watt, comparable to results with (SrMg) (PO :Sn phosphors in lumen output, and white and color rendition. Moreover, phosphors of the invention produce line emission, a desirable characteristic for certain applications. Under cathode-ray excitation, BaY O :Eu gave 9.1 foot-lamberts, when excited at 20 kilovolts with 17.5 microamperes per 35 square centimeters. The color was x=0.'63l, y=0.362 in the ICI color coordinant system.

Ba MgY O :0.03Eu O gives a plaque brightness of about 55% of a standard Eu-activated YVO, phosphor, and Ba CaY O :O.03Eu O gives about 45% in comparison, and Ba ZnY O :0.03Eu gives about 24%.

Activation with Eu gives response to 2537 A. radiation and cathode-ray excitation. Tb, Sm and Dy activators only give response to cathode-ray excitation.

Colors produced with these compositions are the characteristic line emission colors found for the rare earths used and can be generally described as follows:

Ba znY O zEu Red. Ba ZnY o zTb Green. B2l ZnY 0 vDy Yellow. B ZnY O :Sm Salmon red.

Ba CaY O :Eu Red. B MgY O :Eu Red. Ba MgY o zSm Salmon red.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Luminescent material having the molar composition:

aBaO:(cd)Y O 1dEu O wherein:

a is between about 0.8 and 1.2,

is between about 1.00 and 1.25, and d is between about 0.03 and 0.14. 3. Luminescent material according to claim 2 having the molar composition:

BaO I 0.95Y203 I 0.05Eu O 4. Luminescent material according to claim 1 having the molar composition:

tlBaOIbAOZ(Cd)Y203ZdR203 wherein:

A is selected from the group consisting of Mg, Ca

and Zn, R is selected from the group consisting of En, Dy, Sm

and Tb, a is between about 1.6 and 2.4, b is between about 0.8 and 1.3, c is between about 0.8 and 1.3, and d is between about 0.008 and 0.2. 5. Luminescent material according to claim 4 having the following molar composition:

aBaOzbCaO: (cd)Y O :dEu O wherein:

a is between about 1.6 and 2.4, b is between about 0.8 and 1.3, c is between about 1.00 and 1,25, and d is between about 0.03 and 0.14.

5 6 6. Luminescent material according to claim 5 having b is between about 0.8 and 1.3, the molar composition: is between about 1.00 and 1.25, and

ZBaOzCaO:095Y203:QOSEUZOa d 1s between about 0.03 and 0.14.

10. Luminescent material according to claim 9 having 7. Luminescent material accordmg to claim 4 having 5 the molar i i wherein: References Cited a is between about 1.6 and 2.4, b is between about 0.8 and 1.3, FOREIGN PATENTS c is between about 1.00 and 1.25, and 1,347,458 11/1963 France d is between about 0.01? and 0.14 OTHER REFERENCES 8. Luminescent materlal according to clalm 7 havlng the molar composition: lgfsrogerszgsloglgzAspects of the Lumlnescence of Solids,

2BaO:MgO:0.95Y 0 0.05Eu O3 15 9. Luminescent material according to claim 4 having TOBIAS LEVOW Primary Examiner the molar composition: R. D. EDMONDS, Assistant Examiner.

aBaO I I (C'd)Y203 :dE11203 wherein; US. Cl. X.R.

a is between about 1. 6 and 2.4, 252 3014 

